Small-sized optical cables are nowadays available on the market, comprising inside them tapes formed by four optical fibers aligned and embedded into a common coating generally made of acrylate resins, of the same nature as the primary coating of the optical fibers.
Large-sized cables (typically 200-1000 optical fibers) are also available, using ribbons or modules of 8, 12, 16, . . . optical fibers. In particular 8-fiber modules are used, in turn separable into two 4-fiber modules.
The need and utility of the separability is due to the compatibility of the 8-fiber tapes with the widely-circulated 4-fiber tapes with which they can therefore be promiscuously handled, fiber-to-fiber jointed through multiple or single melting or through multiple or single connectors.
In order to be able to easily split the tapes into 4-fiber modules on the field without damaging the optical fibers and without using special tools, several solutions have been adopted. One of these is based upon a double embedding, i.e. two 4-fiber modules are preliminarly assembled and cross-linked and subsequently a common coating is applied around the two flanked modules.
Clearly this solution, besides being expensive because of the double process, entails an increase in size and weight both of the tape and the cable employing
Other solutions are based upon the narrowing of the thickness of the covering resin at the portion of the split line between the two modules.
In one of them, such narrowing is obtained by covering the two optical fibers adjacent to the split line along a longitudinal cross-section of the tape with flexible resin having low Young's modulus and then embedding the whole into rigid resin having high Young's modulus. In such way, at the split line, the thickness of the rigid resin coating becomes smaller. However, also this type of tape has the same drawbacks as the above-mentioned double process solution.
Another solution is based upon the application of a very thin layer of resin (typically 20 micron thick against 50-80 microns generally used) with the expedient of adding a release agent at the line between contiguous optical fibers when the tape is to be split in order to make the resin softer at the separation line during split.
Also this solution has drawbacks since, besides weakening the structure of the tape, the introduction of release agents may give rise to problems, especially in the presence of humidity. In fact, since the acrylate of the coating is a hydrophilic material, the eventual absorption of water into the coating can entail the localization of the same in the discontinuity zone created by the releasing agent with bubble formation which could cause transmission losses due to microbendings of the optical fibers. Moreover, tapes used nowadays still require the use of a specific tool for cutting and/or eliminating flashes.